1. Field of the Invention
The present invention relates to an injection-molded plastic optical lens.
2. Description of the Prior Art
The uneven thickness of a plastic article is one of the important factors that adversely affect the molding result during the plastic injection molding process. After a molten plastic material has been injected into a mold's cavity whose thickness is uneven, the portion of the molten plastic material in a region of the mold with a greater depth likely shrinks during the cooling process because it takes longer to be cooled. Moreover, the portion of the molten plastic material in a region of the mold with a smaller depth will solidify first because it takes less time to be cooled. Consequently, the stress of the solidified portion of the plastic article (in the region of the mold with a smaller depth) will increase and cause warpage in the portion of the plastic article in the region of the mold with a greater depth. Further, the molten plastic material flows through the region of the mold with a greater depth at a speed higher than the speed at which it flows through the region of the mold with a smaller depth, and this may result in filling imbalances. All of the aforementioned problems are resulted from the uneven thickness of the plastic article that adversely affects the molding result during the plastic injection molding process.
Similarly, the thickness of a plastic optical lens is one of the important factors that would influence the injection molding process. A lens generally comprises three portions: an optical effective portion pertaining to the actual optical imaging, a peripheral portion for assembling the lens, and a connecting portion for connecting the optical effective portion and the peripheral portion. Generally, the connecting portion has a thickness substantially the same as that of the optical effective portion and is of a simple shape for connecting with the optical effective portion so that the molten plastic material can favorably fill the lens mold during the injection molding process while achieving a uniform shrinkage. However, when a lens to be formed has a compact size with an extremely thin central region of the optical effective portion thereof, the difference in thickness between the connecting portion and the central region of the optical effective portion is increased, thereby having unsatisfactory molding results as described above. This will seriously affect the image quality of a plastic optical lens for which high precision operation is required.
FIG. 1A is a top view of a prior art plastic optical lens 100. The plastic optical lens 100 comprises, in order from a center to an edge thereof: an optical effective portion 01, a connecting portion 02 and a peripheral portion 03 having a sprue gate portion 104. During the process of manufacturing the plastic optical lens 100 by plastic injection molding, the molten plastic material is injected into a cavity of a mold through a sprue gate corresponding to the sprue gate portion 104. FIG. 1B is a sectional view of the prior art plastic optical lens 100 along the line A-A′ in FIG. 1A. As shown in FIG. 1B, the thicknesses of the optical effective portion 01 and the connecting portion 02 are not uniform, and the connecting portion 02 is thicker than the optical effective portion 01. In other words, the plastic optical lens 100 has a peripheral thickness which is greater than its central thickness. Therefore, an unsatisfactory molding result caused due to the non-uniform thickness of the molded article may occur in the plastic optical lens 100 during the plastic injection molding process and further adversely affect the optical image quality of the plastic optical lens 100.